In a conventional inkjet printer, a printhead can include a series of actuators for ejecting ink onto a substrate. Conventional actuator-based inkjet printers can rely on a multi-step process for jetting. For example, ink is drawn into an ejection chamber where a membrane (also referred to as a diaphragm) is pushed/pulled by the actuator and creates a pressure wave which forces the ink to move. That is, ink is ejected from an actuator nozzle when the diaphragm is released. The printhead can be formed of multiple individual layers, sometimes referred to individually as layers or plates (which can be metal and/or polymer). The plates/layers can be assembled together such as by stacking one plate over the other. The stacked plates/layers form what is referred to as a jetstack.
The jetstack can include internal fluid flow paths/channels through which ink from can flow and be jetted out of the printhead through an aperture plate. One of the plates/layers making up the printhead functions as a particulate filter, and can be a rock screen to protect a jetstack from contamination. Other plates can be designed with particular geometries for maintaining a predetermined ink volume throughout the printhead, and/or directing the flow of ink. For example, in order to properly direct the ink to the ejection chamber, and then from the ejection chamber to the aperture plate, the various jetstack layers may have ink flow holes that, when the layers are stacked one on top of the other, provide fluidic communication between the corresponding openings of adjacent plates, and form a complete fluid path for the ink. The size, geometry and order of the various plates in the jet stack can be limited by the allocated area of the printhead and pressure drop requirements for properly ejecting the ink.
One known method for assembling the various metal layers of a solid ink printhead is to stack them, and then place the stacked layers in a high temperature vacuum furnace while applying pressure to form a diffusion bond between the various metal plates. An advantage of this method is that several layers can be bonded simultaneously. However, this assembly method suffers from a cost disadvantage, in that the individual plates are often plated with a precious metal such as gold to improve the diffusion bond.
Another known assembly method is used for bonding individual layers, such as metal and/or polyimide layers, making up the print head. For example, such layers can be bonded using preformed thin film polymer adhesives that are designed and laser cut to match fine features/geometries of the layers the adhesives are formed between. While the use of polymer adhesive layers can reduce the cost, thin film plastics can be difficult to work with as they are not dimensionally as stable as metal plates, especially under high temperature and pressure. Additionally, moisture take-up/loss can cause dimensional instabilities and thin film polymer adhesives are also flimsy which makes them difficult to align fine features to one another. Finally use of polyimide plates are more prone to carrying contamination from the laser cutting process, and collecting new contamination particles as they have a tendency to generate an electrostatic charge.
In yet other assembly methods, some of the layers used for forming a print head can be stacked and bonded sequentially, or they may be stacked sequentially and then bonded simultaneously. In even yet another assembly method, some layers may be stacked and bonded to one another first and then bonded to another set of layers that were also stacked and bonded. In such a method, those layers that are bonded to one another with higher cure temperature adhesives are required to be bonded first to one another before subsequent layers bonded with lower temperature adhesive are added thereto.
For example, a conventional printhead jetstack 100, such as that shown in FIG. 1, can include a plurality of stacked layers/plates. The plurality of stacked layers/plates can include a diaphragm layer 102, a body plate 104, a vertical inlet 106, a rockscreen 108, a first manifold 110, a second manifold 112, and an aperture plate 137. Body plate 104 can be configured to define an ink chamber (as well as its volume) from which ink is ejected. Vertical inlet 106 can be configured to allow filtered ink into a body chamber (a smaller opening in the body plate) and also is configured to define a starting point (a larger opening in the body plate) of an exit path for the expelled ink. Rockscreen 108 can be configured to filter potentially problematic particulates, such as those capable of blocking or occluding the various ink flow pathways, from the ink. Manifolds 110 and 112 can be configured with a shared reservoir that feeds several individual body chambers of the print head. The jetstack can utilize additional layers/plates, for example, to provide for actuation and/or support to the printhead, such as a flex insulator layer 131, a flex metal 132, another flex insulator 133, an actuator 134, and a thermoplastic adhesive 136.
As described above, in a process for forming the jetstack, some of the plates, such as plates/layers 104, 106 and 108, may be assembled via a diffusion bonding process, wherein each plate is stacked, one on the other, and then diffusion bonded together. That is, one layer, such as body plate 104, can be diffusion bonded to vertical inlet 106, and separately, or in succession, rockscreen 108 can be diffusion bonded to vertical inlet 106. Additionally, diaphragm layer 102 can be diffusion bonded to body plate 104. Upon bonding the layers as described, portions of their individual geometries match-up with those of adjacent layers/plates to form an ink flow path.
It is desirable to reduce the manufacturing costs associated with stacking the layers of a conventional jetstack. As discussed above, one way to reduce the cost is to eliminate the need for diffusion bonding, which relies on the use of precious metals, and use an alternative method for bonding the conventional layers/plates. For example, instead of diffusion bonding the metal plates, they can each be adhesive bonded to an adjacent plate, wherein adhesive is added via spray coating, as is the case for bonding webbed first manifold layer 110 to rock screen 108. However, at least conventional body plate 104, vertical inlet 106 and rockscreen 108 lack appropriate geometries for moving to a process that utilizes only adhesive bonding, even in the case in which it is important that a very thin layer of adhesive be formed on the layers being bonded via adhesive bonding. That is, without the correct geometry, when such layers/plates are placed together for adhesive bonding, excessive adhesive will flow (squeeze-out) from between the layers and flow into the designed ink path, restricting or completely blocking the flow of ink.
While not limited to any particular theory, it is believed that upon the various conventionally designed plates being stacked together, adhesive will tend to accumulate in voids formed on each plate, such as a plate's ink-flow holes. This is due to the active area of geometries of such conventional plates/layers including large surface area of continuous surface surrounding ink-flow holes having a smaller relative area. As shown in FIGS. 2A-2B, the conventional diaphragm includes a surface 101 that includes an active area 103. The active area 103 can include a plurality of ink flow holes 103′, with each ink flow hole 103′ separated by solid surface 101′. As illustrated, not only does the diaphragm's surface comprise a much larger area of the total plate than does the active area, but also the solid surface 101′ comprises a larger area of the active area 103 than do the plurality of ink flow holes 103′. Thus, upon bonding the diaphragm to another conventionally designed layer, such as to a first surface of body layer 104, adhesive is forced into the ink flow paths 103′ as shown by the adhesive obstructions 115, which can be detrimental to the printhead's normal function.
Another problem can occur when adhesive being added to a layer in which the ink flow holes are too small, such as on a conventional vertical inlet layer 106. In such a case, there is a risk that adhesive will fill the ink flow holes while applying/spraying on the adhesive before bonding. For example, as shown in FIGS. 3A-3B, the vertical inlet layer 106 can include a surface 107 of which a portion is an active area 105. The active area 105 can include a plurality of ink flow outlet holes 105′, a plurality of inlet holes 139, and a solid surface 107′ that separates the various ink flow holes 137, 139. Additionally, vertical inlet 106 can include large thru ink feeds 135 that provide an ink flow path from one section of the printhead (e.g., a back section or the top of the printhead in FIG. 1) to another section of the printhead (e.g., a front section or the bottom of the printhead in FIG. 1 where the vertical inlet is fluidically connected to finger manifolds formed by the plates of manifolds 110 and 112). Accordingly, an ink flow path is formed within the jetstack that can be blocked by excess adhesive formed between the layers of the stack. For example, the ink flow path can extend from from the finger manifolds of manifolds 110 and 112 through the rockscreen and through the plurality of smaller openings 139. Upon activation of the piezoelectric actuator 134, ink is forced through the ink flow path that continues from the body chamber through the plurality of larger ink flow holes 105′ of the vertical inlet plate, through a non-reservoir portion of manifold plates 110 and 112, through ink flow openings of a compliant wall 136 and through ink flow openings of a thermoplastic adhesive that is disposed between the compliant wall 136 and aperture plate 137. However, as shown, the active area surface 107′ between i) adjacent ones of holes 105′, ii) adjacent holes 105′ and 139, and iii) adjacent ones of holes 139, has a larger area than the areas of the flow holes. Thus, upon bonding the diaphragm to another conventionally designed layer, such as at a second surface of body layer 104, adhesive can flow into the ink flow holes 105′ and 139′, which can be detrimental to the printhead's normal function.
What is needed, therefore, is a method for assembling a printhead that minimizes or eliminates use of diffusion bonding of jetstack plates or use of preformed adhesive films for bonding layers of a jetstack together.